def get_sample_cases():
    """获取示例测试用例"""
    return [
        ("23", ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]),
        ("", []),
        ("2", ["a", "b", "c"])
    ]

def generate_test_case():
    """生成随机测试用例"""
    import random
    length = random.randint(1, 4)
    digits = ''.join(random.choice("23456789") for _ in range(length))
    return digits